RADICAL-CATION INITIATED CYCLOADDITION OF ELECTRON-RICH ALLENES - EVIDENCE FOR A STEPWISE MECHANISM

Several di- and tri-substituted allenes have been allowed to react wit h pentamethylcyclopentadiene in a radical cation initiated cycloadditi on. Mechanistic evidence points to the occurrence of an intermediate d istonic radical cation, the ring closure of which to the Diels-Alder p roduct radical cations is controlled by the substituent at the remote end of the allene. A novel criterion for the design of stepwise radica l cation cycloadditions is presented.